Fastening device

ABSTRACT

A fastening device, which will facilitate the assembly of associated parts or manufactured articles, and electromagnetic energy absorptive component for absorbing electromagnetic waves and converting wave energy to heat; an expansive component, which expands upon exposure to heat emanating from the target material; matrix material, which will become adhesively active and effect the adherence of the associated parts upon exposure to heat emanating from the target material, and a stiffening component.

CROSS REFERENCE TO A RELATED APPLICATION

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 09/376,172, filed on Aug. 17, 1999 now U.S. Pat.No. 6,543,976, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/072,301, filed on May 4, 1998, now U.S. Pat. No.5,938,386, which is a continuation-in-part of U.S. patent applicationSer. No. 08/642,826 filed on May 3, 1996, now abandoned.

TECHNICAL FIELD

The disclosed invention relates to a fastening device which is useful infacilitating the assembly of associated parts by employing a heatactivated assembly element such as a dowel or a disc or a stripconstructed to include a target material and a solid substance whichwill exhibit adhesive and expansive properties on exposure to heat. Theheat will be generated in the target material by exposing the targetmaterial to electromagnetic waves.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 4,038,120 to Russell describes the use of an energizedheating element or wire to heat a hot melt glue resulting in adhesionbetween contiguously assembled panels. The reference method involvesheating a glue-coated wire to liquefy the glue, producing a cohesivestate and facilitating the assembly of panels. This method is useful forintroducing a cohesive material (glue) to an area of limitedaccessibility (groove), but the heating element (wire) requires thedirect application of energy (electricity) to provide the heat to meltthe glue.

U.S. Pat. No. 3,996,402 to Sindt relates to the assembly of sheetmaterials by the use of a fastening device utilizing an apertured sheetof eddy current-conducting material sandwiched between coatings ofhot-melt glue. An induction heating system is activated causing eddycurrent heating in the EC-conducting material with consequent melting ofthe hot-melt glue thus resulting in fusion and bonding of the sheetmaterials in accordance with the desired construction.

U.S. Pat. No. 3,574,031 to Heller et al. describes a method and materialfor welding thermoplastic bodies by using a susceptor sealant betweenthe bodies to be joined. The susceptor sealant is characterized byhaving particles, heatable by induction, dielectric or radiant energy,dispersed in a thermoplastic carrier compatible with the thermoplasticsheets to be welded. The welding of the thermoplastic sheets is effectedby applying and exposing the susceptor sealant to heat energy, softeningthe carrier material and joining all thermoplastic materials.

U.S. Pat. No. 3,612,803 to Klaas discloses a fastening device, which, inits most relevant embodiment, consists of a quantity of heat-activatableadhesive containing a closed electronically conductive loop and aferromagnetic material insulated from said closed loop. In operation,the fastening device is activated by a solenoid coil energized withalternating electrical current. The current emitted from the solenoid istransferred to the fastening device where a current of large amperageand low voltage is generated in the loop enveloped by theheat-activatable adhesive. The current produces heat that causes theadhesive to become sticky. The efficiency, and apparently theusefulness, of the disclosed device is improved by fitting it with aferromagnetic core enclosed within the closed loop.

SUMMARY OF THE INVENTION

The instantly disclosed fastening device is distinguished from, and goesbeyond, the prior art by describing an assembly element which willprovide structure, strength and stability to an assembled product whileserving as a vehicle for introducing an adhesive material in a neat,non-messy form to internal and inaccessible areas of the parts to beassembled. In addition to providing adhesive properties, the discloseddevice simultaneously expands upon exposure to heat; this expansiontakes up assembly clearances and provides contact pressure at theinterface between the adherends and the device. The disclosed deviceincludes a target material for absorbing and converting electromagneticwaves to heat, and for conducting heat energy to both the expansiveassembly element and the adhesive material so that it can be activatedto provide an adhesive bond between the associated parts. Thisdisclosure also relates to an improved and expeditious method for theassembly and adherence of associated parts of various materials whichare mostly transparent to electromagnetic waves. The improved methodutilizes a device which comprises an assembly element which includes areceptive target material for absorbing electromagnetic waves, a solidadhesive material contiguous with the conductive target material whichwill become physically or chemically adhesive by heat energy resultingfrom electromagnetic waves absorbed and conducted by the targetmaterial, and an expansive material which expands concurrently with theheat from the target material. This disclosure also relates to theassembled products produced according to the method utilizing thedisclosed fastening device.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification, illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a sectional view of the fastening device fashioned into theshape of a dowel;

FIG. 2 is a sectional view of the fastening device in the form of adowel situated and “hidden” within associated parts;

FIG. 3 is a sectional view of the fastening device situated as in FIG. 2and being adhesively activated by electromagnetic waves emanating froman RF source;

FIG. 4 is a partial sectional plan view of the fastening device in theshape of a disc depicting repositories of adhesive material;

FIG. 4 a is a sectional view of the fastening device in the shape of adisk, taken along section line 4 a:4 a of FIG. 4;

FIG. 5 is a sectional view of the fastening device which illustrates theorientation of fibrous material in the condition prior to application ofheat and pressure;

FIG. 6 is a sectional view of the fastening device which illustrates theorientation of fibrous material after application of heat and pressureand subsequent cooling;

FIG. 7 is a sectional view of the fastening device of FIG. 6 assembledwithin an article before activation by electromagnetic waves;

FIG. 8 is a sectional view of the fastening device assembled within anarticle after activation by electromagnetic waves;

FIG. 9 is an alternative embodiment of the fastening device;

FIG. 10 is an alternative embodiment of the fastening device;

FIG. 11 is an alternative embodiment of the fastening device;

FIG. 12 is an alternative embodiment of the fastening device;

FIG. 13 is a sectional view of the fastening device fashioned into theshape of a dowel and including a stiffening component;

FIG. 14 is a sectional view of the fastening device in FIG. 13 situatedand “hidden” within associated pieces;

FIG. 15 is a sectional view of the fastening device fashioned to theshape of a dowel and including rings 52 of expansive component;

FIG. 16 is a sectional view of the fastening device of FIG. 15;

FIG. 17 is a sectional view of the fastening device fastened to theshape of a dowel and including a strip of expansive component;

FIG. 18 is a sectional view of the fastening device of FIG. 17 situatedin and hidden within associated pieces;

FIG. 19 a is a partial sectional plan view of the fastening device inthe shape of a disk depicting depositories of adhesive material andstrips of adhesive components; and

FIG. 19 b is a sectional view of the fastening device in the shape of adisk taken along section line of FIG. 19 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings, wherein like numerals indicate the same elementsthroughout the views.

The disclosed device 10, shown in FIG. 1, features an expansive assemblyelement 13, a target material 12, and coated with a solid adhesivematerial 11. As illustrated in FIG. 2, device 10 is designed to beplaced, in a generally hidden relationship, between or within associatedparts 20 to be adhesively joined. When desirably situated, such as inholes 21 drilled to accommodate a dowel or in grooves cut to accommodatea disc, the device can be exposed to electromagnetic waves 22, generallyemanating from a generator 15 by passing the wand of the generator inthe general area of the “hidden” device, as shown in FIG. 3. Thepreferred range for electromagnetic wave frequency is from approximately100 Hertz (100 Hz) to approximately 10 Megahertz (10 MHz). Theelectromagnetic waves will penetrate the aligned associated parts 20, tobe adhesively joined, said parts being substantially transparent toelectromagnetic waves. The target material must be fashioned fromsubstances which are not transparent to electromagnetic waves, that willabsorb the electromagnetic waves, and create heat which will beconducted to both the solid adhesive material and the expansive assemblyelement. To elaborate, heat is produced in the conductive targetmaterial by two mechanisms: eddy current resistive heating and magnetichysteresis. Eddy current resistive heating applies to all conductivematerials and is produced in the target material by the electromagneticwaves emanating from the generator (sometimes called the inductioncoil). The generator is energized by a traditional source of alternatingcurrent. The heat from magnetic hysteresis is observed only in magneticmaterials. As the electromagnetic field produced by the generatorreverses polarity, the magnetic sites in the target material alsoreverse. There is an energy loss in this reversal which is analogous tofriction; this energy loss is magnetic hysteresis. The “lost” energy isimmediately converted to heat and conducted by the target material toboth the heatactivatable adhesive material to initiate adhesion and tothe expansive assembly element to initiate expansion. When heated to thenecessary temperature, the adhesive material will soften, liquefy orbecome heat-activated, attach itself to the adjacent associated parts,and, on cooling, create an adhesive relationship between the associatedparts.

Two types of adhesives, hot-melt and heat-activated cure, are proposedfor use with the disclosed device. Both types of adhesives are initiatedby heat emanating from the conductive target material. Hot-meltadhesives are solid at ambient temperatures, but melt or liquefy whenthe temperature is elevated by heat flowing from the conductive targetmaterial. The melted adhesive wets the adherends and, in the case ofporous, foraminous, or fibrous adherends, penetrates the surface of theparts to be bonded. As the adhesive cools, the adherends and adhesiveare bonded. In the case of porous, foraminous, or fibrous adherends,mechanical interlocking can contribute to bond strength. Note that forthe hot-melt mechanism, the bonding is reversible. Thus, by repeatingthe induction heating procedure, the bond can be undone and theadherends separated. The ability to reverse the adhesion and separateassembled parts is not a trivial attribute. In addition to the advantageof being able to re-assemble or repair misaligned parts, it is alsodesirable to be able to disassemble manufactured articles to facilitateserviceability and repair. Often, when working with associated parts ofdifferent materials, it will be beneficial to disassociate assembledparts to facilitate recycling. Heat-activated curing adhesives are alsosolid and easy to manipulate at ambient temperatures, but when theadhesive temperature is elevated by the heat from the conductive targetmaterial, a chemical reaction is initiated. This reaction involves acure or crosslinked bonding either within the adhesive or between theadhesive and the adherends. Such bonds are typically irreversible.Frequently, a heat activated curing adhesive bond will demonstrate anelectrostatic attraction between the adhesive and the adherends and acrosslinked bond within itself. In one form of a typical embodiment ofthe disclosed fastening device 10, the adhesive coated target materialcan comprise or be affixed to, or incorporated into, an expansiveassembly element 13, such as a dowel, a strip, or a disc. In onepreferred embodiment as shown in FIG. 1, the assembly device is formed,molded, compressed or machined into a dowel having an annular dam 14 orfitted diameter for containing or localizing the adhesive after it hasliquefied and positioning barbs 16 to help the dowel remain in thedesired alignment. The dowel is then wrapped, coated, surrounded,embedded or integrated with an RF target material 12 fashioned from areadily available RF susceptor such as steel or aluminum.Electromagnetic energy absorptive component 12 may also be disposedwithin the expansive components on the surface of the expansivecomponents, within stiffening components, on the surface of thestiffening components, or within the adhesive material. The solidadhesive material is attached to the foil by a liquid coating orphysical self-attachment in the form of a film, encapsulants, granulesor powder. The fully fabricated device is then inserted in pre-drilledholes 21, aligned between associated parts 20 to be joined and thejoined parts are then exposed to electromagnetic waves 22 from anelectromagnetic wave generator 15 as shown in FIG. 3. The waves mustpenetrate the parts to be joined but all materials, to some extent, aretransparent to electromagnetic waves. Materials that are not astransparent, such as those containing significant amounts of metal, willsimply require a longer or more intensive exposure to theelectromagnetic wave generator and the emanating waves. Then, the targetmaterial absorbs the emanating waves, converts the waves to heat energy,and conducts the heat energy to both the adhesive coating and theexpansive assembly element.

The expansive assembly element 13 is to be fabricated from a variety ofmaterials that exhibit suitable compressibility and mixed with a heatactivated binder material. Suitable compressible materials will beeither fibrous, foraminous, or rubber-like in nature and have suitabletemperature resistance to allow activation of the binder material.Suitable fibrous materials include fiberglass, ceramic fibers, graphitefibers, metal wool, plant fibers, animal bristles, and mixtures of thepreceding. Suitable foraminous materials include sponges, crushednutshells, hollow plastic spheres, and synthetic foam products. Bindermaterials will be either hot melt adhesives or heat curing adhesives.

Alternatively, the expansive component may be derived from the productof a heat activated or enabled chemical reaction, and not necessarily bepre-compressed. Either reaction products from the combination of two ormore materials or decomposition products from one or more components mayproduce a product with a significant or required increase in specificvolume. Such ingredients may or may not be encapsulated. The mostdramatic reaction products will become gases at least at an elevatedtemperature during thermal activation. Upon cooling, an element of theexpansion will remain. Examples include voids in the case of gases andregions of material with overall lower densities, i.e., increasedspecific average volumes.

Alternatively, the expansive component may be derived from a purelyphysical phase change. One or more components may become gaseous atleast at an elevated temperature during thermal activation. Upon coolingor vitrification from chemical reaction, voids may remain as a result ofgaseous expansion. A further example would include encapsulatedmaterials under pressure whose shells collapse or melt as temperatureincreases, allowing a gas to expand or a solid or liquid to phase changeto a gas and to expand.

As shown in FIGS. 13–19 b, one or more stiffening components 15 may beprovided to the fastening device of the present invention to provideadditional rigidity and strength to the assembly. Preferably, thestiffening component 15 is of a strength and rigidity at least as greatas that of the other components of the fastening device. The stiffeningcomponent materials preferably include wood or cellulose fibers, carbon,glass, boron, or other high modulus fibers, engineering thermoplastics,ceramic material, combinations of the aforementioned materials and anyother material of suitable stiffness and durability that does notinterfere with the expansion process or RF energy absorption.Alternatively, the stiffening component may act as a susceptor itself.The stiffening components may be of any suitable configuration to impartdesirable stiffness to the fastening components. For example, thestiffening component may cover a portion or all of the fasteningcomponent. The stiffening component may be of a single, unitary piece ormultiple stiffening components may be provided in a fastening device.The stiffening components may be of a honeycomb or web-like material.Stiffening components may also be expansive to provide for additionaltightness of fit of the fastening device within the associated pieces.Additionally, the stiffening components may contain adhesives or matrixmaterials that advantageously react with heat as well.

FIGS. 13 and 14 depict alternative embodiments of the fastening devicecomprising a substantially longitudinally disposed stiffening component50 disposed within the expansive component 13. FIGS. 15 and 16 show anadditional alternative embodiment wherein rings of expansive material 52are disposed in annular depressions of stiffening component 50. FIGS. 17and 18 depict stiffening components 50 containing a depression thatreceives a strip of adhesive material 52. Although only one suchadhesive strip 52 is shown in FIG. 17 and 18, any number of strips maybe provided to the fastening device 10 in order to impart theappropriate amount of adhesive and tight fit within the associatedpieces 20. Strips of adhesive material 52 may be substantially linear ormay be disjointed and/or curvilinear. As shown in FIGS. 4 and 4A, theassembly device may comprise a device in the shape of a disk, includingrepositories or channels for directing adhesive material. Additionally,as shown in FIGS. 19 a and 19 b, the disk may be comprised substantiallyof stiffening components 50 and may include one or more strips ofadhesive components 52.

The operation of the fastening device is illustrated in FIG. 5 throughFIG. 8. Note that for presentation purposes, the expansive assemblyelement 13 is shown to be a fibrous material, although the operation ofthe device would be the same for other materials. In FIG. 5, thefastening device 10 is shown before compression of the expansiveassembly element 13. The fastening device 10 after compression of theexpansive assembly element 13 is shown in FIG. 6. The compression isachieved by applying heat and pressure to the expansive element 13 untilthe adhesive binder material within element 13 is activated then coolingsufficient to harden the binder material in order to fix the element inthe compressed state. The fastening device 10 is placed withinassociated parts 20 to be adhesively joined in FIG. 7. Note that inorder to assure that the mating line 24 of the assembly is minimized, aclearance 23 is provided. Upon exposure to electromagnetic waves, thetarget element 12, which is an RF susceptor material such as steel,absorbs same and converts the energy to heat which is conducted to boththe adhesive 11 and the expansive assembly element 13. Concurrently, theadhesive is activated and the element expands. The expansion of thefastening device takes up the assembly clearance 23 and transports theadhesive to the adherent surface. The resultant pressure from theexpansion of the device is beneficial both in the adhesive bonding andin increasing the bond strength by friction.

Alternative embodiments of the fastening device are illustrated in FIG.9, FIG. 10, FIG. 11, and FIG. 12. In FIG.9, the fastening device 10consists of a target material 12 surrounded by an expansive assemblyelement 13 on both sides. In FIG. 10, the fastening device 10 is shownwith three target material layers 12 which could reduce the time neededto heat the adjacent expansive assembly elements 13 sandwiched betweenthem. In certain applications, this configuration could be extended toan indefinite number of target material layers. An expansive assemblyelement which incorporates the target element function is shown in FIG.11. Here, the target material 13 would be either metallic fibers,particles, or flakes. Alternative target materials would includeconductive (metallic or organic) materials, inherently conductiveparticles (ICP's), and semiconductive materials such as graphite andsilicon, in the form of fibers, flakes or particles. The fasteningdevice 13 could also be mixture of suitable compressible materials withsuitable target materials and an adhesive binder material. In FIG. 12,the fastening device 10 consists of two adhesive layers 11 sandwiching acomposite expansive assembly element 13 of FIG. 11.

In laboratory experiments with an assembly device as disclosed here, afiberglass mat originally 0.188 inches thick was heated in an oven witha film of a polyamide hot melt adhesive on top. The oven temperature wasset at 450° F., which is slightly above the melting point. Upon meltingthe adhesive was absorbed into the fiberglass. The hot adhesive wettedmat was removed from the oven, sandwiched between two sheets of aluminumfoil and placed in a press. Pressure was applied until the adhesive wasobserved to be solidified. Thickness was measured to be 0.100 inches.The lamination was then heated using electromagnetic waves with afrequency of approximately 100,000 hertz (100 kHz) until expansion ofthe lamination was observed. The lamination continued to expand afterremoval of the heating source. Upon cooling the lamination thickness wasmeasured at 0.147 inches.

Immediate needs for the disclosed fastening device have been identifiedin the furniture industry where neat, effective and efficient assemblymethods can readily be exploited to manufacture affordable units in afast, effective and clean manner. Furniture and cabinet manufacturingapplications will involve the assembly of associated parts of wood andplastic, both of which are transparent to electromagnetic waves andreceptive to adhesive bonding. Other uses for the disclosed deviceinclude the fabrication of lattice panels, the installation of trimmolding and fence erection. Also envisioned is the assembly of plywood,gypsum board and combination boards to wall ceiling and floor framingmaterials. In the packaging industry, there is a need to facilitate thefast and effective construction of containers made of wood, plastic, andengineered fiber base materials, which could all be readily assembledusing the disclosed device. In addition to the simplest configuration ofthe fastening device where the assembly element is a disc, dowel orstrip coated with an adhesive material, other configurations of thefastening device are also envisioned. One such configuration features afastening device comprising an expansive assembly element providingalignment and support to assembled associated parts, a conductive targetmaterial integrated with the expansive assembly element, for absorbingelectromagnetic waves and an adhesive material, contiguous with the RFsusceptor material, becoming adhesively active by heat energy resultingfrom the electromagnetic waves absorbed and conducted by the targetmaterial.

While the foregoing is a complete description of the disclosed method,numerous variations and modifications may also be employed to implementthe purpose of the invention. And, therefore, the elaboration providedshould not be assumed to limit the scope of the invention that isintended to be defined by the appended claims.

1. A fastening device for promoting the assembly and adherence of associated pieces by exposure to electromagnetic energy, said fastening device having an outer surface and comprising: (i) an electromagnetic energy absorptive component comprising an electromagnetic energy absorptive target material; (ii) an expansion component adapted to be expansive in at least one direction upon exposure to heat, said expansion component being in a compressed state which compressed state is released upon exposure to heat; and (iii) a matrix material component comprising a matrix material, said matrix material being adhesively activatable by heat energy; wherein the matrix material comprises or is disposed on the outer surface of the fastening device and the matrix material, the expansion component and the electromagnetic energy absorptive component are oriented so that heat generated in the electromagnetic energy absorptive component is conducted to the matrix material and expansion component whereby when said fastening device is positioned within said associated pieces and is exposed to electromagnetic energy, said electromagnetic energy absorptive component provndes heat energy to activate said expansion component and said matrix material, thereby causing said matrix material to either soften or liquefy as well as become adhesively active and allowing or causing the expansion component to expand in at least one direction causing contact of said matrix material and said associated pieces, thereby effecting ajoining or bonding relationship upon cooling of said matrix component.
 2. The fastening device of claim 1 wherein the expansion component is held in a state of compression by a reversible heat activated binder material.
 3. The fastening device of claim 2 wherein the heat activated binder material is a hot melt adhesive.
 4. The fastening device of claim 2 wherein the heat activated binder material is activated at temperatures the same as or lower than the activation temperature of the matrix material.
 5. The fastening device of claim 1 wherein the expansion component is selected from the group consisting of fibrous, foraminous and rubber-like materials.
 6. The device of claim 3, wherein the expansion component is a fibrous material selected from a group consisting of fiberglass, ceramic fibers, graphite fibers, metal wools, plant fibers, animal fibers, polymer fibers and mixtures thereof.
 7. The device of claim 3, wherein the expansion component is a foraminous material selected from a group consisting of sponges, crushed nut shells, hollow plastic spheres, ground cork, synthetic foam, and mixtures thereof.
 8. The device of claim 1, wherein said eleciromagnetic energy absorptive component is selected from the group consisting of a metallic foil, a metallic fibrous material, conductive metal particles, metallic flakes, conductive organic material, conductive magnetic material, inherently conductive particles, and mixtures thereof.
 9. The fastening device of claim 1, wherein said electromagnetic energy absorptive component is disposed in at least one of the following ways; on an outer surface of said expansion component, within said expansion component, on an outer surface of said matrix material component, and within said matrix material component.
 10. The device of claim 1, wherein said matrix material is a hot melt adhesive.
 11. The device of claim 1, wherein said matrix material is a heat activatable adhesive.
 12. A fastening device for promoting the assembly and adherence of associated pieces by exposure to electromagnetic energy, said fastening device having an outer surface and comprising: (i) an electromagnetic energy absorptive component which generates heat as a result of the eddy current resistive heating upon exposure to electromagnetic energy; (ii) an expansion component adapted to be expansive upon exposure to heat in at least one direction, said expansion component being selected from the group consisting of compressed fibers, compressed foraminous materials and compressed rubber-like materials, which materials release from their compressed state upon exposure to heat; and (iii) a matrix material component selected from the group consisting of hot melt adhesives and heat activated adhesives; wherein the matrix material comprises or is disposed on the outer surffice of the fastaing device and the matrix material, the expansion component and the electromagnetic energy absorptive component are oriented so that heat generated in the electromagnetic energy absorptive component is conducted to the matrix material and expansion component whereby when said fastening device is positioned within said associated pieces and is exposed to electromagnetic energy, said electromagnetic energy absorptive component provides heat energy to activate said expansion component and said matrix material, thereby causing said matrix material to either soften or liquefy as well as become adhesively active and allowing or causing the expansion component to expand in at least one direction causing contact of said matrix material and said associated pieces, thereby effecting a joining or bonding relationship upon cooling of said matrix component. 